1. Field of the Invention
The present invention relates generally to electrical enclosures. The present invention relates particularly to protection of the enclosure and components therein from arc blast damage with a strong, fast arc blast vent.
2. Discussion of Related Art
Metal clad switch gear cabinets are parts of the electrical distribution equipment chain designed to provide a compartmentalized cabinet for protection of the distribution equipment such as circuit breakers, bus bars, transformers, and related control equipment and the environment and people surrounding the equipment.
Short circuits or other uncontrolled electrical conduction within the cabinet can create an arc which results in a plasma and rapidly expanding arc gases, a so-called arc blast, which may burn through the cabinet or destroy its utility/safety by expansion of the metal skin and or frame of the cabinet.
As arcs occur it is important to quickly vent these gases to the outside of the cabinet. Within the known art there are several types of mechanisms for the venting of arc gases to the outside of the cabinet.
Any electrical cabinet subject to arcing and arc blast pressures such as switch gear, switch board, motor control centers, etc. to be considered “arc resistant” may need venting for the superheated arc gases and associated particulates.
ANSI Type 1 and Type 2 arc resistant switch gear both vent arc gases and associated particulates out the top of the cabinet. See ANSI/IEEE C37.20.7-2007; EEMAC G14-1987 and IEC 62271-200. Given these requirements, any venting “flue” should also be covered with a strong flap to prevent contamination of the interior of the cabinet or accidental deformation inward from objects or people contacting the vent cover, while providing a quick acting vent opening to the outside of the cabinet. Therefore, the arc blast vents must be strong to bear an inwardly directed load of, e.g., being stepped on by installers or maintenance workers.
In one type of vent cover known in the art, plates of metal, often called flaps, have one or more edges fastened or integral with the top structure of the cabinet. The free edges of the flaps allow the flaps to be bent upwardly under the arc gas pressure to create the vent opening.
In the known art there are arc blast vent such as shown in U.S. Pat. No. 6,407,331 to Smith et al., which creates the flaps from a solid top sheet which is cut to form the free edges of the flaps. The top sheet area creating the flaps is then reinforced underneath with additional structure. There are also arc blast vents for equipment like SQUARE D brand Motor Control Center and Power Zone 4 cabinets having a cut out vent area which leaves integral top plate structure which is then overlaid with rectangular flaps fastened to the top plate.